THEGREENGROK    Planetary Watch

Planetary Watch: Weird Science, Weird Creatures

by Bill Chameides | October 27th, 2008
posted by Erica Rowell (Editor)

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This “giant” spearhead-shaped biologically grown magnetite crystal may have been part of a larger organism with many spearheads oriented as star points radiating from a center hub. (Photo Credit: McGill University)

Every once in a while a paper comes by that is so “out there” you just gotta take note. Here’s one.

The Context

A fascinating event in the Earth’s history occurred about 55 million years ago: the planet experienced a large jump in global temperatures, getting 5 degrees Celsius warmer in fewer than 10,000 years (see here). This temperature rise is called the Paleocene-Eocene Thermal Maximum (PETM) because it happened on the cusp between the Paleocene and Eocene Epochs (the Eocene was a time when mammalian groups experienced great diversification).

Scientists are not completely sure what caused the PETM, but it seems fairly certain that large releases of greenhouse gases (carbon dioxide and/or methane) were a major factor. You might find that fact a little sobering, as we try to suss out the long-term implications of the present greenhouse gas rise, resulting this time from our own actions.

The Creature

A team of scientists report in the Proceedings of the National Academy of Sciences that they have found the fossil of a unique creature from this past hothouse Earth — a “giant” magnet-making microorganism that may have evolved and flourished only during the PETM.

What Is It?

Yup, believe it or not, there are creatures that make magnets. They are called “magnetotactic,” or magnet-making, microorganisms. Today the vast majority of them are magnetotactic bacteria that live in sediments on the ocean floor or in lakes where there is little oxygen (see here and here).

First discovered in the 1960s, these magnets are thought to provide the bacteria with the ability to orient themselves along the Earth’s magnetic field, endowing them with an elegant, one-dimensional way to navigate their oxygen-poor aquatic environments. When exposed to more toxic, oxygen-rich conditions, for example, the magnet would appear to act as a “head-down-into-the-mud” directional compass enabling bacteria to find their way to safer, oxygen-poor environments.

Magnetotatic bacteria may have lived 2 billion years ago, but definitive fossils of these creatures date back 70 million years ago to the Cretaceous period.

Once these creatures died, they left behind a crystalline magnet. In the fossil record these are called “magnetofossils.” Most magnetofossils are composed of iron and oxygen in the form of the mineral magnetite. Until recently, all the magnetofossils that had been found were on the order of a few tens of nanometers in size (a nanometer is one billionth of a meter) to a few hundred nanometers — the size associated with magnet-making bacteria.

But now, scientist D. Schumann from McGill University and his colleagues have found a magnetofossil that is a few thousand nanometers long. By magentofossil standards that is a humongous fossil and way too big to be from a magnet-making bacterium. The magnetofossil may be the remains of a single-celled eukaryote — a more complicated microorganism that evolved from bacteria, the main difference being that eukaryote cells have a nucleus (read more about eukaryotes).

An Ideal Environment

Schumann and colleagues believe that conditions during the PETM might have been so favorable that magnet-making organisms were able to diversify, allowing ever stranger and larger organisms to evolve. For example, with a significantly hotter, wetter Earth, the continental shelf off the U.S. Mid-Atlantic coast (where the fossils were found) would have had high rates of erosion. This would have supplied the additional iron necessary for the organisms to grow larger magnetite crystals than more commonly found magnetotactic counterparts either before or after this time.

Looking to the Past for an Idea of the Future

In the case of global warming, scientists often look to the geologic past to provide clues as to what we might encounter in the future. During the PETM it is estimated that some 30–40 percent of the creatures living on and in the ocean sediments went extinct. At the same time, Schumann’s research suggests that a giant magnetic-forming creature evolved and then expired when temperatures cooled.

It seems that major environmental upheavals can create lots of losers and a space where opportunists can fill the void. Some might find it interesting to ponder who or what might rise to fill the void of homo sapiens should we as a species be so unfortunate to shuffle “off this mortal coil.”

filed under: animals, climate change, faculty, global warming, Planetary Watch
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